It has become common to view a book provided as electronic data in a given form (hereinafter referred to as “electronic book”), via an electronic device capable of displaying the electronic data. At least the following facts (1) through (3) appear to form backgrounds of such a rapid diffusion: (1) the electronic book has a great advantage that, unlike a conventional book printed on paper, the electronic book occupies no physical space and is not subjected to aged deterioration, (2) performance of the electronic device has been improved and price-reduction comes along, and (3) advance in computer network technology causes a change in distribution mechanism.
With the rapid diffusion, importance of the improvement in performance of the electronic device has been further increased. Particularly, in a field of information science, attempts have been widely made to improve convenience for a user in terms of software. For example, Patent Literature 1 discloses a method of causing a terminal to display an image content with a plot. With the method, it is possible to display an image in order of the plot while changing a display magnification in accordance with a size of the content.